Convergence device for color television



ct. EL w67 F. A. WOOD CONVERGENCE DEVICE FOR COLOR TELEVISION Filed Dec. 27, 1965 l INV/SN'IUR. f Frank AWoOd AT'rorney United States Patent (")iifice 3,348,177 Patented Oct. 17, 1967 3,348,177 CONVERGENCE DEVICE FOR CULOR TELEVISION i Frank A. Wood, Elmhurst, Ill., assigner to Zenith Radio Corporation, Chicago, Ill., a corporation of Delaware Filed Dec. 27, 1965, Ser. No. 516,356 9 ciaims. (el. ass- 213) The subject invention relates, in general, to color television but more particularly to electromagnetic convergence apparatus for use with tri-beam color reproducing cathode ray tubes.

A cathode ray tube of the type employed in conventional color television receivers comprises a delta array of electron guns which generate and direct a trio of electron beams towards the target structure of the tube. The target includes a luminescent screen comprising an ordered grouping of red, green and blue phosphor dots. These phosphor dots are arranged in a plurality of primary color triads, i.e. each triad is formed of a red, a green and a blue phosphor dot. Disposed adjacent the screen is a mask having a like plurality of apertures, one in registration with each color triad.

During scansion, the three beams must substantially converge at or near the plane of the aperture mask if proper color reproduction is to be achieved. When properly converged the three beams instantaneously illuminate only the phosphor dots included within a particular triad.

The geometry of a shadow-mask tube, however, is such that the three beams do not naturally converge at all points of the raster during scansion. Normally, static as well as dynamic convergence is required. To achieved such convergence it is known to subject the beams to auxiliary magnetic fields. Static convergence is conventionally accomplished by the use of permanent magnets which are adjustably supported about the neck of the tube. These magnets direct their flux toward pole piece pairs mounted within the neck section of the tube. These pole pairs are so located as to shunt the elds of the magnets across the paths of the electron beams.

Dynamic convergence, on the other hand, is attained by resort to electromagnetic apparatus which also directs its iluX into the internal pole pieces. These electromagnets are energized by correction signals derived from the horizontal and vertical deflection circuits. This electromagnetic apparatus, as well as the permanent magnets, are commonly mounted on a yoke which is adjustably positionable about the neck of the tube.

A typical prior art electromagnetic convergence device comprises a U-shaped core having a vertical and a horizontal convergence winding mounted in tandem on each leg of the core. The tandem relationship has been employed in order to reduce undesired coupling between adjacent horizontal and vertical windings. On the other hand, the realizable flux density attainable in such cores, and thus the eiiiciency of the device, is partially determined, by the length of core enclosed by the winding. Prior art electromagnetic convergence devices, therefore, have reflected a compromise insofar as coupling and eciency considerations are concerned.

It is therefore a general object of the invention to provide an improved convergence apparatus for use with multi-beam color reproducing cathode ray tubes.

It is a specific object of the invention to provide a more eicient electromagnetic device for use in dynamic convergence apparatus.

- In accordance with the invention an electromagnetic device for use with convergence apparatus employed with a multi-beam cathode ray tube having a pole piece pair associated with each beam, comprises a core of magnetic material which has a pair of legs. Each of the legs comprises a rst section of predetermined cross-sectional area and a contiguous second section of a different crosssectional area. The extremities of the second sections which are remote from the first sections are disposed in a spaced apart relation, confront an assigned pair of pole pieces and establish a non-magnetic gap therebetween. A pair of horizontal convergence windings are individually mounted upon and substantially encompass an assigned one of the reduced leg sections of the core. Additionally, a pair of vertical convergence windings are individually mounted upon and substantially encompass the length of an assigned one of the legs and overlap one of the horizontal convergence windings. Means are provided for serially connecting each of the horizontal convergence windings in a flux-aiding relation as are means for serially connecting each of the vertical convergence windings in a flux-aiding relation.

The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description .taken in conjunction with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is an elevational view, partly in section, of a preferred embodiment of the invention positioned about the neck of a 1nulti-beam cathode ray tube.

FIGURE 2 is a sectional view of an electromagnet device embodying the invention.

FIGURE 3 is a cross-sectional view taken along line 3-3 of FIGURE 2.

FIGURE 4 is a schematic diagram showing the electrical circuitry of the convergence coils of the embodiment shown in FIGURES l and 2; and

FIGURE 5 is a perspective View of an alternate core construction for the electromagnetic shown in FIGURES l and 2.

A convergence apparatus 10 embodying a form of the invention s depicted in FIGURE l. As there shown the convergence apparatus is mounted upon the neck 11 of a tri-beam cathode ray tube of the type employed in conventional color television receivers. In color reproducing tubes of this type, the longitudinal axis of neck 11 is coincident with the geometric axis of the tube itself. A trio of electron guns (not shown) are symmetrically disposed about this axis and develop the electron beams 12, 12' and 12". Supported within the neck portion of the tube and extending radially from the tube axis are pairs of metallic pole pieces 13, 13 and 13". These pole pairs, which are spaced around the tube axis on centers, present outer faces 14, 14', 14" to electromagnetic devices which are housed within convergence apparatus 10 and which will be more fully described below. The inner extremities of pole pairs 13, 13', 13, on the other hand, confront respective ones of electron beams 12, 12 and 12". While apparatus 1t) is disclosed as possessing particular utility with mutli-beam tubes having internal pole pieces, this apparatus can also be employed with multi-beam tubes without such pole piece provision. A Y-shaped magnetic shield 15 is interposed between the internal pole pieces to prevent interaction of the magnetic fields developed across them.

Convergence apparatus 10 is of an interlocking tripartite construction comprising three substantially identical equally spaced lobes 16, 16', 16". Each such lobe includes an arcuate wall section having a curvature conforming to the wall of tube neck 11. A U-shaped spring 17 secures apparatus 10 at a desired location upon the tube neck, that is, with each of lobes 16, 16', 16 positioned over an assigned one of pole pairs 13, 13', 13, respectively.

each of lobes 16, 16', 16 18 (only two shown) Individually associated with are static convergence magnets which are mounted in holders 19 adjustably supported upon outside walls of the lobes. With this arrangement the flux fields of the permanent magnets are presented to the outer faces 14, 14', 14" of the internal pole pieces.

Each of lobes 16, 16', 16" houses identical structure for dynamically converging its assigned beam; therefore discussion will be confined to a consideration of lobe 16, the internal structure of which is detailed for this purpose. Accordingly, and as best shown in FIGURES 1 and 2, lobe 16 houses an electromagnetic device 20 comprising a U- shaped core 21 of magnetic material having a pair of parallel legs 22. Core 21 is preferably constituted of a high permeability material such as ferrite, although other high permeability materials are also suitable. Each of core legs 22 comprises a first section 23 having a predetermined cross-sectional area and contiguous second section 24 having a reduced cross-sectional area. The free extremities of leg sections 24 are canted to accommodate the curvature of neck 11 Aof the cathode ray tube and are disposed in a spaced apart confronting relating to the outer faces of the pole pieces 13, 13', 13". In this fashion a non-magnetic air gap is established between the free ends of the core legs and the internal pole pieces.

A pair of horizontal convergence windings 26 are iudividually mounted upon and encompass reduced leg sections 24. Additionally, a pair of vertical convergence windings 27 are individually mounted upon and encompass substantially the entire length of leg sections 23. As best illustrated in FIGURE 2 each of vertical windings 27 overlap the horizontal winding occupying the same core leg.

Preferably, windings 26, 27 are wound upon the coil forms 28, 29, respectively, not only to facilitate assembly of device 20 but also to provide a predetermined spacing between the windings and thus control the degree of coupling between the coils, particularly in the region where they overlap, see FIGURES 2 and 3.

As schematically shown in FIGURE 4 the end turns of the horizontal convergence windings 26 are serially connected in a flux-aiding relation. In like fashion, the end turns of the vertical convergence win-dings 27 are serially connected in a flux-aiding relation. The free ends of windings 26 and 27 are returned, respectively, to horizontal and vertical deflection circuits, not shown.

In operation, convergence apparatus is mounted upon the neck of the picture tube and positioned so that electromagnets 20 and the permanent magnets 18 are in juxtaposition with assigned ones of internal pole pieces 13, 13', 13". As already indicated, each of the electron beams passes between the confronting ends of an assigned pair of pole pieces. The magnetic field extending across the ends of each pair of pole pieces is substantially perpendicular to the trajectory of the beam, thus producing a lateral deflection of the beam which is proportional to the strength of the impressed field. By controlling the strength of these magnetic field-s, the beam trajectories are altered so that the beams converge at a given point on the tube screen.

In the absence of a control signal to the dynamic convergence windings 26, 27, the flux passing through the internal pole pieces is determined by permanent magnets 18. The strength of these fields is determined by the orientation and the proximity of the magnet to the internal pole pieces. Accordingly, to achieve `static convergence of the three beams, magnets 18 are adjusted until the desired degree of convergence is attained.

Dynamic convergence of the electron beams, on the other hand, is accomplished by electromagnets 20. More particularly, horizontal and vertical convergence windings 26, 27 are energized by control signals derived from the deflection system, which signals vary as functions of the horizontal and vertical scanning signals, respectively. These control signals develop time-varying magnetic ux fields within core 21. This field is directed through then URES 1-3:

Leg section 23, length L in 1.05 Leg section 24, length l in .37 Leg section 23 cross-sectional area in.2 .0625 Leg section 24, cross-sectional area in.2 .0256 Horizontal winding 26 No. 38 gauge Vertical winding 27 No. 35 gauge While the core legs are disclosed as substantially square in cross-section, this construction is not imperative but was employed in the operative embodiment since it is a feasible configuration in which to mold ferrite material. A core having a circular configuration would be equally suitable. To achieve the optimum benefits of the invention, the core legs should be of equal length and the length l of leg section 24 should be about one-third the length L of leg section 23, and the cross-sectional area of leg section 24 should be about 40 percent of the cross-sectional area of leg section 23', however these length and area ratios may -be varied within a range of approximately i30 percent to adapt the device for picture tubes of different characteristics and to conform to differing space requirements in various receiver designs. Moreover, while each of horizontal and vertical windings 26, 27 are layer type windings, other winding configurations may be employed with equal success.

FIGURE 5 shows an alternate construction for the core of electromagnet 20. This core, designated by reference numeral 30, is a two piece construction and is formed by butting together a pair of L-shaped core legs 31. A non-magnetic spacer 32 is inserted between the abutting faces of the core legs. Each of core legs 31 comprises a first section 33 having a predetermined cross-sectional area and a contiguous second section 34 having a reduced cross section. As in the principal embodiment, the free extremities of sections 34 are disposed in a spaced apart relation so as to confront adjacent pole faces of the internal pole pieces.

Except for the non-magnetic gap established at the junctions of the L-shaped legs, core 30 is similar in other respects to core 21. Convergence windings of identical construction can be mounted upon core 31 so that, in operation, an electromagnet employing a core 31 construction functions in the same fashion as electromagnet 20 does for dynamic convergence.

The presence of the non-magnetic gap in the bight of core 30 does, however, permit use of a different static convergence arrangement. More particularly, a static convergence arrangement for use with an electromagnet empolying a core of the type shown in FIGURE 5 may employ a disc shaped permanent magnet. A permanent magnet of this configuration is magnetized across its diameter and mounted adjacent the bight of core 30 and preferably in a plane parallel to the core.

In operation, static convergence is accomplished by rotating the disc type permanent magnet so as to alter the permanent magnetic field established in the core by the magnet. This field, of course, is introduced into the internal pole pieces of the tube to alter the trajectory of the beam and accomplish static convergence in the manner discussed above. Dynamic convergence is accomplished in the same manner as described above for the electromagnet 20.

In each embodiment of the invention there is provided an improved core and winding arrangement for a dynamic convergence device. The described core construction permits the vertical convergence coil to extend along substantia-lly the entire length of a core leg thereby increasing the sensitivity of electromagnet 20. Undesired cou* pling between the vertical and horizontal convergence windings is kept to a tolerable degree by confining the horizontal winding 'beneath one end of the vertical winding and by establishing a predetermined spacing between the windings in the area where they overlap.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a convergence apparatus for use with a multibeam cathode ray tube having a pole piece pair associated with each electron beam, an electromagnetic device for selectively positioning one of said lbeams comprising:

a core of magnetic material having a pair of legs;

each said leg comprising a first section of predetermined cross-sectional area and a contiguous second section of reduced cross-sectional area relative to that of said first section;

the extremities of said second sections remote from said first sections being disposed in a spaced apart relation and adapted to confront an assigned pair of said pole pieces when said convergence apparatus is mounted on said tube;

a pair of horizontal convergence windings individually mounted upon and encompassing an assigned one of said reduced leg sections;

a pair of vertical convergence windings individually mounted upon and encompassing substantially the entire length of an assigned one of said first leg sections and overlapping one of said horizontal convergence windings;

means for serially connecting each of said horizontal convergence windings in a linx-aiding relation;

and means for serially connecting each of said vertical convergence windings in a iiuX-aiding relation.

2. An electromagnetic beam positioning device as defined in claim 1, in which said core of magnetic material is U-shaped and in which the legs are substantially parallel.

3. An electromagnetic beam positioning device as defined in claim 1, in which said vertical convergence windings completely overlap said horizontal convergence windings.

4. An electromagnetic beam positioning device as defined in claim l, in which said second sections of said core legs have a uniform cross-'sectional area,

5. An electromagnetic beam positioning device as defined in claim 1, in which said first and second sections of said core legs each have a uniform cross-sectional area.

6. An electromagnetic beam positioning device as defined in claim 2, in which said Uashaped core is provided With a non-magnetic gap in its bight portion.

7. An electromagnetic beam positioning device as defined in claim 1, in which said legs are of approximately equal length and the length of the second leg section of each of said legs is approximately one-third the length of its associated first leg section.

li. An electromagnetic beam positioning device as defined in claim 1, in which the cross-sectional arca of the second leg section of each of said legs is approximately forty percent of the cross-sectional area of its associated first leg section.

9. In a convergence apparatus for use with a multibeam cathode ray tube having a pole piece pair associated with each electron beam, an electromagnetic device for selectively positioning one of said beams comprising:

an U-shaped core of magnetic material having a pair of substantially parallel legs;

each said leg comprising a first section of predetermined uniform substantially square cross-sectional area and a contiguous second section of reduced uniforrn substantially square cross-sectional area relative to that of said first section;

the extremities of said second sections remote from said first sections vbeing disposed in a spaced apart relaiton and adapted to confront an assigned pair of said pole pieces when said convergence apparatus is mounted on said tube;

said legs being approximately equal in length and the length of said second leg section of each of said legs being approximately one-third the length of its associated first leg section;

the cross-sectional area of said second leg section of each of said legs being approximately 40% of the cross-sectional area of its associated rst leg section;

a pair of horizontal convergence windings individually mounted upon and encompassing an assigned one of said reduced leg sections;

a pair of vertical convergence windings individually mounted upon and encompassing substantially the entire length of an assigned one of said first leg sections and completely overlapping one of said horizontal convergence windings;

means for serially connecting each of said horizontal convergence windings in a flux-aiding relation;

and means for serially connecting each of said vertical convergence windings in a liux-aiding relation.

References Cited UNITED STATES PATENTS l/1947 Buckbee 335-213 6/1965 Patti 335-213 X 

1. IN A COVERGENCE APPARTUS FOR USE WITH A MULTIBEAM CATHODE RAY TUBE HAVING A POLE PIECE PAIR ASSOCIATED WITH EACH ELECTRON BEAM, ELECTROMAGNETIC DEVICE FOR SELECTIVELY POSITIONING ONE OF SAI DBEAMS COMPRISING: A CORE OF MAGNETIC MATERIAL HAVING A PAIR OF LEGS; EACH SAID LEG COMPRISING A FIRST SECTION OF PREDETERMINED CROSS-SECTIONAL AREA AND A CONTIGUOUS SECOND SECTION OF REDUCED CROSS-SECTIONAL AREA RELATIVE TO THAT OF SAID FIRST SECTION; THE EXTREMITIES OF SAID SECOND SECTIONS REMOTE FROM SAID FIRST SECTIONS BEING DISPOSED IN A SPACED APART RELATION AND ADAPTED TO CONFRONT AN ASSIGNED PAIR OF SAID POLE PIECES WHEN SAID CONVERGENCE APPARATUS IS MOUNTED ON SAID TUBE; A PAIR OF HORIZONTAL CONVERGENCE WINDINGS INDIVIDUALLY MOUNTED UPON AND ENCOMPASSING AN ASSIGNED ONE OF SAID REDUCED LEG SECTIONS; A PAIR OF VERTICAL CONVERGENCE WINDINGS INDIVIDUALLY MOUNTED UPON AND ENCOMPASING SUBSTANTIALLY THE ENTIRE LENGTH OF AN ASSIGNED ONE OF SAID FIRST LEG SECTIONS AND OVERLAPPING ONE OF SAID HORIZONTAL CONVERGENCE WINDINGS; MEANS FOR SERIALLY CONNECTING EACH OF SAID HORIZONTAL CONVERGENCE WINDINGS IN A FLUX-AIDING RELATION; AND MEANS FOR SERIALLY CONNECTING EACH OF SAID VERTICAL CONVERGENCE WINDINGS IN A FLUX-AIDING RELATION. 